U.S. patent application number 10/431399 was filed with the patent office on 2004-11-11 for electroformed sputtering target.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Dickerson, Scott, Subramani, Anantha K., Vesci, Anthony.
Application Number | 20040222088 10/431399 |
Document ID | / |
Family ID | 33416445 |
Filed Date | 2004-11-11 |
United States Patent
Application |
20040222088 |
Kind Code |
A1 |
Subramani, Anantha K. ; et
al. |
November 11, 2004 |
Electroformed sputtering target
Abstract
A method of fabricating a sputtering target for sputter
depositing material onto a substrate in a sputtering chamber is
described. In one embodiment of the method, a preform having a
surface is formed and a layer of sputtering material is
electroplated onto the surface of the preform to form the target.
The method can be applied to form a sputtering target having a
non-planar surface.
Inventors: |
Subramani, Anantha K.; (San
Jose, CA) ; Vesci, Anthony; (San Jose, CA) ;
Dickerson, Scott; (Fremont, CA) |
Correspondence
Address: |
APPLIED MATERIALS, INC.
Patent Department, M/S 2061
P.O. Box 450A
Santa Clara
CA
95052
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
33416445 |
Appl. No.: |
10/431399 |
Filed: |
May 6, 2003 |
Current U.S.
Class: |
204/298.12 ;
204/298.13; 205/170; 205/182 |
Current CPC
Class: |
C23C 14/3414
20130101 |
Class at
Publication: |
204/298.12 ;
205/170; 205/182; 204/298.13 |
International
Class: |
C23C 014/34 |
Claims
What is claimed is:
1. A method of fabricating a sputtering target, the method
comprising: (a) forming a preform having a surface; and (b)
electroplating a layer of sputtering material onto the surface of
the preform, thereby forming the sputtering target.
2. A method according to claim 1 wherein (b) comprises
electroplating a layer of at least one of copper, aluminum,
tantalum, titanium and tungsten.
3. A method according to claim 1 wherein (a) comprises forming a
preform comprising at least one of aluminum, copper, steel and
titanium.
4. A method according to claim 1 wherein (a) comprises forming a
preform having a surface that is non-planar.
5. A method according to claim 4 wherein (a) comprises forming a
preform comprising an annular inverted trough about a central
cylindrical well and (b) comprises electroplating a layer of
sputtering material on a surface of the annular inverted trough and
central cylindrical well.
6. A method according to claim 1 wherein the method further
comprises: (c) removing at least a portion of the preform from the
electroplated layer to expose an underlying surface of the
electroplated layer, and electroplating a second layer of
sputtering material onto the underlying surface.
7. A sputtering target comprising an electroplated layer of
sputtering material.
8. A target according to claim 7 wherein the electroplated layer of
sputtering material comprises at least one of copper, tantalum,
titanium and aluminum.
9. A target according to claim 7 wherein the electroplated layer of
sputtering material comprises a non-planar surface.
10. A target according to claim 7 wherein the target comprises an
annular inverted trough about a central cylindrical well.
11. A target according to claim 7 wherein the electroplated layer
comprises grains having a grain size of from about 10 .mu.m to
about 100 .mu.m.
12. A target according to claim 7 comprising multiple electroplated
layers.
13. A sputtering method comprising: (a) placing a substrate in a
sputtering chamber; (b) providing a sputtering target comprising an
electroplated layer of sputtering material; (c) providing a process
gas in the sputtering chamber; and (d) electrically biasing the
target relative to a wall or support in the chamber to energize the
process gas to sputter material from the target onto the
substrate.
14. A method according to claim 13 wherein (b) comprises providing
a sputtering target comprising an electroplated layer having a
non-planar sputtering surface.
15. A sputtering chamber comprising: (a) a substrate support; (b) a
sputtering target facing the substrate support, the sputtering
target comprising an electroplated layer of sputtering material;
(c) a gas delivery system to provide a gas in the chamber; (d) a
gas energizer to energize the gas to sputter the sputtering
material from the sputtering target and onto the substrate; and (e)
an exhaust system to exhaust the gas.
16. A chamber according to claim 15 wherein the electroplated layer
of sputtering material comprises a non-planar sputtering
surface.
17. A chamber according to claim 16 wherein the non-planar
sputtering surface is on a sputtering target comprising an annular
inverted trough about a central cylindrical well.
18. A chamber according to claim 15 wherein the electroplated layer
comprises least one of copper, aluminum, tantalum, titanium and
tungsten.
19. A chamber according to claim 15 wherein the electroplated layer
comprises grains having a grain size of from about 10 .mu.m to
about 100 .mu.m.
20. A chamber according to claim 15 wherein the electroplated layer
comprises multiple electroplated layers.
Description
BACKGROUND
[0001] The present invention relates to sputtering targets and
their methods of manufacture.
[0002] A sputtering chamber is used to sputter deposit material
onto a substrate to manufacture electronic circuits, such as for
example, integrated circuit chips and displays. Typically, the
sputtering chamber comprises an enclosure wall that encloses a
process zone into which a process gas is introduced, a gas
energizer to energize the process gas, and an exhaust port to
exhaust and control the pressure of the process gas in the chamber.
The chamber is used to sputter deposit a material from a sputtering
target onto the substrate, such as a metal for example, aluminum,
copper, tungsten or tantalum; or a metal compound such as tantalum
nitride, tungsten nitride or titanium nitride. In the sputtering
processes, the sputtering target is bombarded by energetic ions,
such as a plasma, causing material to be knocked off the target and
deposited as a film on the substrate.
[0003] In one version, a sputtering target may be formed by holding
a sheet of spin-formed sputtering material against the surface of a
target backing plate and diffusion-bonding the sputtering material
to the backing plate by hot isostatic pressing. However, this
method has several disadvantages. The sputtering material required
to form the spin-formed sheet typically has to have a high level of
purity, and consequently, is expensive. Target fabrication costs
are driven even higher because both surfaces of the sheet of
sputtering material are typically machined smooth to facilitate
diffusion bonding to the underlying backing plate as well as to
provide a smooth exposed sputtering surface. Targets formed by such
a method can be undesirable because they can have a grain structure
that is sheared by the forces generated in the spin-forming
process, resulting in non-uniform grain sizes. Also, the targets
can have undesirable pores and voids occurring in the bond between
the backing plate and sputtering material. During processing, the
non-uniform grain size and voids of the target can generate
sputtered deposits that are non-uniform or uneven in thickness. The
non-uniform and uneven deposition of the sputtered material can
result in processed substrates having inferior quality, and can
even damage structures formed on the substrate.
[0004] It is also difficult to form sputtering targets having
convoluted or complex shapes using conventional processes. Targets
having complex shapes are often used to provide enhanced sputtering
coverage in magnetic fields, as described for example in U.S. Pat.
No. 6,274,008 to Gopalraja et al., "Integrated Process for Copper
Via Filling," commonly assigned to Applied Materials, which is
incorporated herein by reference in its entirety. Such targets may
comprise for example ridges, projections, rings, troughs, recesses
and grooves. Conventional processes such as the spin forming
process are not satisfactory in forming complex target shapes,
because a significant amount of machining is required to cut out
the desired convoluted shape from the spin formed layer. This
machining is costly and wastes the expensive high purity sputtering
material. Also, excessive machining can generate shearing forces on
the surface of the target which plastically deform the grains on
the target surface to produce an undesirable surface grain
structure.
[0005] Thus, it is desirable to form sputtering targets having more
uniform and consistent grain surface structure and with fewer
voids. It is further desirable to form sputtering targets having
complex or non-planar shapes reproducibly and with reduced
costs.
SUMMARY
[0006] A sputtering target comprises an electroplated layer of
sputtering material.
[0007] In a method of fabricating a sputtering target, a preform
having a surface is formed, and a layer of sputtering material is
electroplated onto the surface of the preform, thereby forming the
sputtering target.
[0008] Another sputtering method comprises placing a substrate in a
sputtering chamber, providing a sputtering target comprising an
electroplated layer of sputtering material, providing a process gas
in the sputtering chamber, and electrically biasing the target
relative to a wall or support in the chamber to energize the
process gas to sputter material from the target onto the
substrate.
[0009] A sputtering chamber comprises a substrate support, a
sputtering target facing the substrate support, the sputtering
target comprising an electroplated layer of sputtering material, a
gas delivery system to provide a gas in the chamber, a gas
energizer to energize the gas to sputter the sputtering material
from the sputtering target and onto the substrate, and an exhaust
system to exhaust the gas.
DRAWINGS
[0010] These features, aspects, and advantages of the present
invention will become better understood with regard to the
following description, appended claims, and accompanying drawings
which illustrate examples of the invention. However, it is to be
understood that each of the features can be used in the invention
in general, not merely in the context of the particular drawings,
and the invention includes any combination of these features,
where:
[0011] FIG. 1a is a partial sectional schematic side view of a
version of a substrate processing chamber;
[0012] FIG. 1b is a partial sectional schematic side view of a
magnetron suitable for the chamber of FIG. 1a;
[0013] FIGS. 2a through 2d are partial sectional schematic side
view illustrating stages in electroforming the sputtering target;
and
[0014] FIG. 3 is a partial sectional schematic side view of a
version of an electroplating apparatus for electroforming a
target.
DESCRIPTION
[0015] An exemplary version of a chamber 106 capable of sputter
depositing material on a substrate 104 is schematically illustrated
in FIG. 1a. The chamber 106 is representative of a self-ionized
plasma chamber, such as an SIP+ type chamber, developed by Applied
Materials, Inc. of Santa Clara, Calif. A typical chamber 106
comprises enclosure walls 118 that include sidewalls, 120, a bottom
wall 122 and a ceiling 124. A substrate support 130 is provided to
support a substrate 104 in the chamber 106. The substrate support
130 may be electrically floating or may be biased by a pedestal
power supply 210, which may be for example an RF power supply 203.
The substrate 104 is introduced into the chamber 106 through a
substrate loading inlet (not shown) in a sidewall 120 of the
chamber 106 and placed on the support 130. The support 130 can be
lifted or lowered by support lift bellows (not shown) and a lift
finger assembly (also not shown) can be used to lift and lower the
substrate 104 onto the support 130 during transport of the
substrate 104 into and out of the chamber 106.
[0016] A process gas, such as a sputtering gas, is introduced into
the chamber 106 through a gas delivery system 150 that includes a
process gas supply 152 comprising gas sources 154a-c that each feed
a conduit 156a-c having a gas flow control valve 158a-c, such as a
mass flow controller, to pass a set flow rate of the gas
therethrough. The conduits 156a-c feed the gases to a mixing
manifold 160 in which the gases are mixed to from a desired process
gas composition. The mixing manifold 160 feeds a gas distributor
162 having one or more gas outlets 164 in the chamber 106. The gas
outlets 164 may pass through the chamber sidewalls 120 to terminate
about a periphery of the substrate support 130. The process gas may
comprise a non-reactive gas, such as argon or xenon, that
energetically impinges upon and sputters material from a target
111. The process gas may also comprise a reactive gas, such as one
or more of an oxygen-containing gas and a nitrogen-containing gas,
that are capable of reacting with the sputtered material to form a
layer on the substrate 104. Spent process gas and byproducts are
exhausted from the chamber 106 through an exhaust system 168 which
includes one or more exhaust ports 170 that receive spent process
gas and pass the spent gas to an exhaust conduit 172 in which there
is a throttle valve 174 to control the pressure of the gas in the
chamber 106. The exhaust conduit 172 feeds one or more exhaust
pumps 176. Typically, the pressure of the sputtering gas in the
chamber 106 is set to sub-atmospheric levels.
[0017] The sputtering chamber 106 further comprises a sputtering
target 111 facing a surface 105 of the substrate 104. The target
111 can be a planar target (not shown) or a non-planar target
(shown). The sputtering chamber 106 can also comprise a shield 128
to protect a wall 118 of the chamber 106 from sputtered material,
and typically, to also serve as an anode with respect to the
cathode target 111. The shield 128 may be electrically floating or
grounded. The target 111 is electrically isolated from the chamber
106 and is connected to a target power supply 200, such as a pulsed
DC power source, but which may also be other types of voltage
sources. In one version, the target power supply 200, target 111,
and shield 128 operate as a gas energizer 180 that is capable of
energizing the sputtering gas to sputter material from the target
111. The target power supply 200 applies a bias voltage to the
target 111 relative to the shield 128. The electric field generated
in the chamber 106 from the voltage applied to the sputtering
target 111 energizes the sputtering gas to form a plasma that
energetically impinges upon and bombards the target 111 to sputter
material off the target and onto the substrate 104. A suitable
pulsing frequency of a pulsed DC voltage for energizing the process
gas may be, for example, at least about 50 kHz, and more preferably
less than about 300 kHz, and most preferably about 100 kHz. A
suitable DC voltage level to energize the process gas may be, for
example, from about 200 to about 800 Volts.
[0018] The chamber 106 further comprises a magnetron 300 comprising
a magnetic field generator 301 that generates a magnetic field near
the target 111 of the chamber 106 to increase an ion density in a
high-density plasma region 226 adjacent to the target 111 to
improve the sputtering of the target material, as shown in FIGS. 1a
and 1b. An improved magnetron 300 may be used to allow sustained
self-sputtering of copper or sputtering of aluminum, titanium, or
other metals--while minimizing the need for non-reactive gases for
target bombardment purposes, as for example, described in U.S. Pat.
No. 6,183,614 to Fu, entitled "Rotating Sputter Magnetron
Assembly"; and U.S. Pat. No. 6,274,008 to Gopalraja et al.,
entitled "Integrated Process for Copper Via Filling," both of which
are incorporated herein by reference in their entirety. The
magnetic field extends through the substantially non-magnetic
target 111 into the sputtering chamber 106. In one version, the
improved magnetron 300 comprises a magnetic field generator 301
having magnets 307 that extend along one or more sidewalls of the
target 111 and are connected by a magnetic yoke 310, as shown in
FIG. 1a. The magnets 307 may comprise one or more of an inner
magnet and outer magnet that are connected together by a yoke 310
that is formed of a magnetically soft material. The magnetic field
generator 301 comprising the magnets 307 provides an enhanced
magnetic field 309 in the region 226 enclosed by the target
sidewalls, thereby increasing the density of the plasma in the
region 226. In another version, the magnetron 300 comprises a motor
306 to rotate the magnetron 300 about a rotation axis 312 to
provide an enhanced magnetic field, as shown in FIG. 1b. The motor
306 is typically attached to the magnetic yoke 310 of the magnetron
300 by a shaft 308 that extends along the rotation axis 312.
[0019] The chamber 106 can be operated by a controller 311
comprising a computer that sends instructions via a hardware
interface to operate the chamber components, including the
substrate support 130 to raise and lower the substrate support 130,
the gas flow control valves 158a-c, the gas energizer 180, and the
throttle valve 174. The process conditions and parameters measured
by the different detectors in the chamber 106, or sent as feedback
signals by control devices such as the gas flow control valves
158a-c, pressure monitor (not shown), throttle valve 174, and other
such devices, are transmitted as electrical signals to the
controller 311. Although, the controller 311 is illustrated by way
of an exemplary single controller device to simplify the
description of present invention, it should be understood that the
controller 311 may be a plurality of controller devices that may be
connected to one another or a plurality of controller devices that
may be connected to different components of the chamber 106--thus,
the present invention should not be limited to the illustrative and
exemplary embodiments described herein.
[0020] In one version, a target 111 suitable for use in a
sputtering chamber 106 comprises a complex shape, such as a shape
comprising a non-planar surface 24, as shown in FIGS. 1a and 1b.
The target 111 is typically circularly symmetric with respect to a
main vertical axis of the chamber 106, and may comprise ridges,
projections, rings, troughs, recesses, grooves or other topological
features that enhance processing of the substrates 104. A target
111 having a complex shape has been discovered to provide improved
sputtering properties, as described for example in aforementioned
U.S. Pat. No. 6,274,008. The target 111 having the complex shape
provides improved process performance by accommodating magnets 37
in proximity to and surrounding high density plasma regions 226
adjacent to the target 111, as shown in FIGS. 1a and 1b, or by
otherwise providing for an enhanced magnetic field 309 that allows
for a large thickness or volume of a sputtering plasma in high
density plasma regions 226 adjacent to the target 111. The target
111 having the complex shape may also serve to improve deposition
uniformity by regulating the effective target area to which
portions of the substrate are exposed. For example, a recessed
portion of the target 111, such as a trough 8, may be effectively
hidden from regions of the substrate 104 that are more distant from
the recessed portion, such as an outer edge 103 of the substrate
104, and thus deposition of material from the recessed portion onto
the more distant regions of the substrate 104 may be reduced.
[0021] The target 111 comprises an inverted annular trough 8
comprising cylindrical outer and inner sidewalls 4,6 and a top wall
5 that at least partially enclose a high density region 226. The
annular trough 8 encircles a central portion of the target 111
comprising a cylindrical well 7 that projects downwards towards the
surface 105 of the substrate 104. The cylindrical inner sidewall 6
defines the sides of the cylindrical well 7, and the cylindrical
well 7 is capped by a bottom wall 9 that faces the substrate 104.
The bottom wall 9 and top walls 5 can be substantially parallel to
the surface 105 of the substrate 104, and the inner and outer
sidewalls 4,6 can be substantially perpendicular to the surface 105
of the substrate 104. At least a portion of the surface 24 of the
side, top and bottom walls 4,5,6,9, comprises the sputtering
material to be sputtered on the substrate 104. The inverted annular
trough 8 and cylindrical well 7 can accommodate magnets 307
positioned between the outer sidewall 4 of the trough and the
sidewall 120 or ceiling 124 of the chamber enclosure 118 and even
within the space enclosed between the bottom and sidewalls 9, 6 of
the cylindrical well 7 and ceiling 124 of the chamber enclosure
118, thereby providing an enhanced magnetic field 309 in the
regions 226 adjacent to the target 111. The target 111 may further
comprise a flange portion 13 that extends radially outward from the
outer sidewall 4 to attach the target 111 to the chamber enclosure
walls 118, for example by vacuum sealing the flange portion 13 of
the target 111 between the ceiling 124 and sidewalls 120 of the
chamber 106.
[0022] The target 111 can be formed in an electroforming process in
which sputtering material is electroplated to form a complex or
non-planar shape. Electroforming provides a sputtering material
having a high purity and good grain properties, such as a higher
uniformity of grain size. Electroforming can also generate a
unitary sputtering material structure having fewer pores or voids.
The method is suitable for forming targets 111 having sputtering
material comprising, for example, one or more of copper, aluminum,
tantalum, titanium and tungsten. The method generally comprises
forming a preform 14 having a surface 16 and electroplating a layer
12 of sputtering material onto the surface 16 of the perform to
form the sputtering target 111. FIGS. 2a through 2d schematically
illustrate stages in an embodiment of a target fabrication
process.
[0023] The target preform 14 provides a support structure on which
the layer 12 of sputtering material can be electroplated, as shown
in FIG. 2a. The preform 14 can comprise the same or a different
material than the sputtering material. In one version, the preform
14 comprises a material that is more easily shaped than the
sputtering material, and may also be of lower purity or less
expensive than the sputtering material. The preform 14 is desirably
formed from a material that is readily electroplated by the
sputtering material, such as for example, a conducting or
semiconducting material that can serve as an anode in an
electroplating process. A suitable preform 14 may comprise, for
example a metal, such as at least one of aluminum, copper, steel
and titanium. For example, the preform 14 may comprise an
industrial grade copper alloy. In one method of forming the preform
14, the metal material is heated to a molten state and poured into
a mold having the desired preform shape. Cooling of the molten
metal in the mold results in the preform 14 having the desired
shape. The molded metal can also be machined or otherwise shaped to
form features in the target preform 14.
[0024] The preform 14 can comprise a complex shape, such as a
non-planar bottom surface 16, that at least partially defines the
shape of the layer 12 of sputtering material electroplated over the
surface 16. In the version shown in FIG. 2a, the preform 14
comprises an inverted annular trough 8 and central cylindrical well
7 having inner and outer cylindrical sidewalls 6,4 that are
positioned to from a partially obtuse angle with the top wall 5 of
the trough 8 such that the cylindrical sidewalls 6,4 form an angle
with respect to one another of from about 5.degree. to about
30.degree., thus forming a trough 8 having a width that narrows
towards the top wall 5 of the trough 8. The preform 14 having the
complex shape serves as a support structure for the formation of
the non-planar electroplated layer 12.
[0025] Sputtering material is electroplated onto the preform 14 to
form the electroplated layer 12 via an electroplating process. In
the electroplating process, one or more surfaces of the preform 14,
such as one or more of the top and bottom surfaces 25,16 is exposed
to an electroplating bath solution 403 in an electroplating
apparatus 405, as shown in FIG. 3. The electroplating solution
comprises an aqueous solution having electrolytes comprising the
sputtering material dissolved therein. For example, the
electroplating solution may comprise one or more of a
copper-containing solution, such as CuSO.sub.4, an
aluminum-containing solution, such as AlSO.sub.4, a
tantalum-containing solution, a titanium-containing solution and a
tungsten-containing solution. A bias voltage is applied to the
surface 16 of the preform 14 via a voltage source 400 that is
electrically connected to the surface 16 of the preform 14. The
voltage source 400 is also connected to an electrode 404 that is in
electrical communication with the surface 16, for example via the
conducting electroplating solution 403. The electrode 404, may
comprise an inert material or may be at least partially formed from
a sputtering material, such as copper. The bias voltage from the
voltage source induces the build up of a negative charge on the
surface 16 of preform 14. This negative charge reduces dissolved
ions and electrolytes in solution containing the sputtering
material to their elemental state at the surface 16 of the preform
14, thereby forming the layer 12 of electroplated sputtering
material on the surface 16. In other words, the sputtering material
is "plated out" on the surface 16 of the preform 14. For example,
copper ions from a copper sulfate electrolyte dissolved in solution
are reduced to elemental copper at the surface 16 of the preform 14
upon application of the bias voltage, thereby "plating out" a layer
12 of copper on the surface 16 of the preform 14.
[0026] The shape of the electroplated layer 12 at least partially
conforms to the shape of the underlying surface 16 of the preform
14. For example, for a preform 14 having a non-planar surface 16,
such as that shown in FIG. 2a, the electroplated layer 12 formed on
the surface 16 also comprises a non-planar surface 18, and may
comprise a complex shape comprising the inverted annular trough 8
and central cylindrical well 7. Thus, the shape of the surface 16
of the preform 14 is at least partially transferred to the
electroplated layer via the electroplating process. The
electroplated layer may be grown on the surface 16 to a thickness
of, for example, from about 0 .mu.m to about 1 .mu.m, such as about
0.5 .mu.m. The thickness of the electroplated layer may even be at
least about 0.5 .mu.m, and even at least about 1 .mu.m.
[0027] The conditions maintained during the electroplating process,
such as the concentration and composition of the electrolytes, the
applied bias voltage, the pH of the bath solution and the
temperature of the solution may be selected to provide an
electroplated layer 12 having the desired composition and
structure. Also, in addition or as an alternative to an aqueous
(water-based) electroplating solution, the solution can comprise an
organic solvent. In one version of a suitable electroforming
process, sputtering material comprising elemental copper is formed
on the non-planar surface 16 of the perform 14 by immersing the
surface 16 in an aqueous solution comprising from about 150 to
about 300 g/L CuSO.sub.4.5H.sub.2O, and even from about 210 to
about 214 g/L CuSO.sub.4.5H.sub.2O. The solution further comprises
from about 30 g/L to about 100 g/L H.sub.2SO.sub.4, and even from
about 52 g/L to about 75 g/L H.sub.2SO.sub.4. The electrode 404 can
be formed from wrought phosphorized copper or oxygen free copper
(OFC). The temperature of the solution is maintained at from about
15.degree. C. to about 45.degree. C., and even from about
21.degree. C. to about 32.degree. C. A bias voltage is applied at a
power level sufficient to provide a current density of from about
0.5 A/dm.sup.2 (amps per decimeter squared) to about 20 A/dm.sup.2,
and even from about 1 A/dm.sup.2 to about 10 A/dm.sup.2. A batch
electroforming process can be performed to simultaneously form the
electroplated layer 12 on a number of performs 14, such as from
about 10 to 20 preforms 14.
[0028] In one version, at least a portion of a surface of the
preform 14 may be masked to inhibit the electroplating of the
sputtering material onto the surface. Masking of the surface allows
for selective plating of the sputtering. For example, as shown in
FIG. 2b, a mask 17 may be provided to at least partially cover the
top surface 25 of the preform 14 to allow electroplating of the
sputtering materials substantially only on the bottom surface 16 of
the preform 14. In one version, the surface may be masked by
applying a less conductive material, such as a polymer or other
dielectric material, to the surface to be masked. The less
conductive material inhibits the build-up of charge on the surface
25, thereby inhibiting the reduction of sputtering materials in the
solution onto the surface 25 of the preform 14. Masking of one or
more surface may be particularly desirable in cases where the
preform 14 has a complex shape or non-planar shape in which
exposure of the surface to be electroplated may also expose other
surfaces of the preform 14. The mask 17 can be subsequently removed
after an electroplating step is performed
[0029] Following electroplating of the sputtering material, the
surface 18 of the electroplated layer 12 can be cleaned in a wet or
dry cleaning process. The cleaning process removes particulates and
other impurities from the surface 18 of the electroplated layer 12.
In one version, the surface 18 of the electroplated layer is
cleaned in a wet cleaning process comprising an acid rinse. In the
acid rinse, the surface 18 is immersed in an aqueous acidic
solution such as HCl, to remove particulates from the surface 18 of
the layer 12. A de-ionized water rinse can also be performed to
remove any particulates loosened from the substrate 104 during the
acid rinse and neutralize any remaining acid. The surface of the
electroplated layer 12 can also be cleaned by an ultrasonic rinse
that dislodges any loose particulates from the surface of the layer
via ultrasonic vibrations. The surface of the electroplated layer
12 can further be machined or otherwise polished before or after
the cleaning steps to provide a smooth surface 18 for the
sputtering process.
[0030] The electroplated layer 12 of sputtering material provides
several advantages. Because the electroplated sputtering material
is "grown" from the surface 16 of the preform 14, the layer 12 of
sputtering material has a high uniformity of sputtering material
grain size. For example, a layer 12 having a uniform sputtering
material grain size of from about 10 to about 100 .mu.m can be
achieved. This high grain size uniformity increases the uniformity
of the layers of material sputtered onto the substrate 104, and
reduces the occurrence of undesirably large grains or "clumps" or
sputtering material that could damage or contaminate the substrate
104. The electroplated sputtering material grown on the surface 16
of the preform 14 forms a strong bond to the preform 14 and forms a
continuous and unitary structure through out the layer 12, thus
reducing the incidence of pores and voids in the layer 12 and
between the layer 12 and preform 14. A further advantage is that
machining of the top surface 25 of the preform 14 and bottom
surface 16 of the electroplated layer 12 is not required to bond
the electroplated layer 12 to the preform 14. Yet another advantage
of the method of fabricating the target 111 is that a target 111
having a complex shape may be manufactured substantially without
extensive machining of a costly bulk sputtering material to form a
target 111 having the desired shape, by "growing" the sputtering
material on a surface 16 of a preform 14 comprising a complex shape
that is at least partially transferred to the overlying conformal
electroplated layer 12.
[0031] In one version, at least a portion of the preform 14 is
removed following formation of the electroplated layer 12. The
preform 14 is desirably at least partially removed to expose a
portion of a top surface 22 of the electroplated layer 12. In one
version, the preform 14 is even substantially entirely removed from
the electroplated layer 12 to expose substantially the entire top
surface 22 of the electroplated layer 12, as shown for example in
FIG. 2c. Desirably, the portion of the preform 14 is removed by a
method that allows for removal of at least a portion of the preform
14 substantially without damaging the electroplated layer 12. The
preform 14 can be at least partially removed by, for example,
machining away portions of the preform 14 from the electroplated
layer 12.
[0032] A subsequent electroplating process can be performed to
electroplate one or more additional layers 20a,b of sputtering
material onto the original or first layer 12, as shown for example
in FIG. 2d. The subsequent electroplating process allows for the
formation of an electroplated target 111a comprising a desired
thickness of sputtering material. The additional layers 20a,b of
sputtering material are electroplated on at least one of the top
surface 22 and the bottom surface 18 of the first electroplated
layer 12. The sputtering material can be electroplated on the top
surface 22 of the first layer 12 and on portions of the bottom
surface 18 of the first layer 12 that have been exposed by removal
of the preform 14 from the layer 12. In one version, a portion of
the top or bottom surface can be masked to selectively electroplate
material substantially on only one of the surfaces. In another
version, both the top and bottom surfaces 22,18 of the first layer
12 are electroplated, as shown for example in FIG. 2d. The
subsequent electroplated layers 20a,b are "grown" out of the first
electroplated layer 12 via the electroplating process, and thus the
first electroplated layer 12 and subsequent electroplated layers
20a,b form a unitary and continuous structure that is absent a
discrete and sharp crystalline boundary therebetween, as
schematically illustrated in FIG. 2d with a dotted line.
Accordingly, the electroplated layers 12, 20a,b form a strongly
bonded and continuous target structure 113 have enhanced
properties, such as improved grain size uniformity and fewer pores
or voids.
[0033] The subsequent layers 20a,b may be electroplated at varying
rates along the surface of the first layer 12 having the non-planar
surfaces 18,22 and complex shape shown in FIGS. 2b through 2d. The
layers 20a,b are electroplated at a faster rate on the "open"
regions of surfaces 18,22 of the non-planar layer 12, such as on
bottom surface 18 of the bottom wall 9 of the cylindrical well 7
and on the top surface 22 of the upper walls 5 of the inverted
annular trough 8, where the open shape of the first electroplated
layer 12 allows better access of reactive ions and electrolytes in
the electroplating solution to the surfaces 18,22 of the layer 12.
Portions of the first non-planar layer 12 such as the bottom
surface 18 of the top wall 5 and top surface 22 of the bottom wall
9 grow the electroplated layer at a slower rate due to the
proximity of inner and outer sidewalls 6,4 surrounding these
regions that at least partially restrict the flow and access of
reactive ions and electrolytes to these surfaces. Because of this
electroplating rate distribution, the growth of the subsequent
electroplated layers 20a20b forms inner and outer target structure
sidewalls 6,4 that are more perpendicular to the surface 105 of the
substrate 104 and bottom and top walls 9,5 of the target than the
original target preform sidewalls 6,4, thereby providing the
desired target shape, as shown for example in FIGS. 2d and 1a
through 1b. The electroplating process may be performed to grow a
layer 20b of sputtering material on the top surface 22 of the first
layer 12 comprising a thickness of from about 0.1 .mu.m to about 1
.mu.m, such as about 0.5 .mu.m, and may even be at least about 0.5
.mu.m, and even at least about 1 .mu.m. A layer 20a of sputtering
material may be grown on the bottom surface 18 of the first
electroplated layer 12 via the electroplating process to a
thickness of from about 0.1 .mu.m to about 1 .mu.m, such as about
0.5 .mu.m, and may even be at least about 0.5 .mu.m, and even at
least about 1 .mu.m.
[0034] The subsequent layers 20a,b may be applied in an
electroforming process comprising the same process conditions, such
as electrolyte concentration, bias voltage, pH and temperature, as
in the first electroforming process to electroplate the first layer
12, or may comprise different process conditions. A suitable
duration of the electroforming process to form the electroformed
layer may be from about 12.5 to about 25 hours. Following the
electroplating process, the target 111 comprising the multiple
layers 12, 20a,b of sputtering material may be further machined to
provide the desired target dimensions and to provide a smooth
target surface 24 and may also be cleaned to remove particulates
from the surface 24.
[0035] The above described method provides a target 111 comprising
one or more electroplated layers 12, 20a,b having improved
properties in the processing of substrates. The method is suited
for the formation of targets 111 having planar or non-planar
surfaces 24 and may even be performed to fabricate targets having
complex convoluted shapes, such as the target 111 shown in FIGS.
1a,b and 2d. Although the present invention has been described in
considerable detail with regard to certain preferred versions
thereof, other versions are possible. For example, the present
invention could be used to form targets having other shapes than
those specifically mentioned, and could be used to form targets
comprising other sputtering materials besides those mentioned. The
process chamber 106 may also comprise other equivalent
configurations as would be apparent to one of ordinary skill in the
art. Thus, the appended claims should not be limited to the
description of the preferred versions contained herein.
* * * * *